This invention relates to the readout of and the writing to an optical disc and more particularly to a method and apparatus for performing these functions in parallel through the utilization of a multiple quantum well device.
Advances in semiconductor technology over recent decades have led to ever increasing capability. With this capability comes the need to process ever more data. Closely related to this need is the need to store and to retrieve data at ever increasing rates and quantities. There have been numerous technical advances in the technology of storing and retrieving data, but these approaches have been largely incremental.
The development of significant improvements in read/write technology, not only will improve the efficiency of data transfer to and from a storage medias such as an optical disc, it will also enable applications which can use the improved read/write technology across a wide variety of industries due to the increased ability to access information.
Nowhere is this more important than in the optical disc field. Here, either DVD discs or CDROM discs are presently read out in a serial fashion by a single read head. Likewise encoding or writing to optical discs is presently accomplished by a single write head. The utilization of a single head moved in a spiral pattern above an optical disc leads to the ability to transmit data only in a serial manner such that many revolutions of the optical disc are required to transfer data.
There thus exists the problem of how to decrease the time it takes to perform a read function of an optical disc. Existing DVD and CDROM systems operate by sensing the contents of tracks. The tracks are semi-circular segments of the disc from which the DVD or CDROM is made. To read the entire contents requires many rotations of the DVD or CDROM. What is needed is a way to decrease the time it takes to read the contents of a DVD or CDROM.
Moreover, there is a problem of how to simultaneously read and write data onto an optical disc. Existing technology requires that reading and writing to a disc be done sequentially. Doing so consumes considerable time. What is needed is a way to read and write simultaneously to a disc.
Moreover, there is a requirement to reduce the number of moving parts related to the transfer of data to and from an optical disc. Currently available optical discs have a laser read/write assembly that spirals in and out to address all of the tracks on the disc. This motion requires two degrees of freedom, and hence includes complexity that a system with a single degree of freedom lacks. What is needed is a way to reduce the number of degrees of freedom so that fewer moving parts are required.
Of course with improved technology there is a possibility of reducing the power required for read/write operations to an optical disc. Reducing power used to write new data to an optical disc is desirable in part for economic reasons, but mostly for reliability issues. What is needed is a way to reduce the power required for read/write operations on an optical disc.
As illustrated in U.S. Pat. Nos. 5,679,947; 5,066,138; 5,305,299; 5,786,947; 5,737,284; and, 5,987,001 there have been many systems devised for reading to an optical disc and writing to it.
U.S. Pat. No. 5,679,947 describes an optical device having a light emitter and a photo sensor, whereas U.S. Pat. No. 5,066,138 refers to the use of holographic elements. U.S. Pat. No. 5,305,299 describes a support mechanism for an optical block in optical disc drive, whereas U.S. Pat. No. 5,786,947 describes an optical pick up device for condensing light from a light source on a single recording surface. Finally U.S. Pat. No. 5,737,284 describes a rapid access to a target track within a program area, whereas U.S. Pat. No. 5,987,001 describes an optical disc drive changer.
It will be appreciated that none of the above reference describe parallel read/write capabilities and as such do not offer the advantages of parallel capabilities in so far as reading and writing to an optical disc.
In the subject invention, parallel read/write capability is provided by the use of a multiple quantum well modulator/emitter/detector device which functions in either one of the three modes dependent upon biasing. These devices are located in a linear array over the surface of an optical disc. In one embodiment, the devices are paired so that the first of the devices operates as a light source, whereas the second of the devices in the linear array operates as a detector of the light reflected from the surface of the disc. It will thus be seen that data can be read from the disc in parallel, with the linear array of devices in one embodiment numbering 1000. This means that the linear array extends radially across the top surface of the disc from the periphery to the center of the disc.
Because of the multiple functionality of the device, the devices can be co-located into what is termed hereinafter a bi-linear array. This multiple functionality is achieved in one embodiment through the utilization of a multiple quantum well device which responds to biasing to determine its function.
For gallium arsenide multiple quantum well devices it has been found that the switching via biasing can be made to occur as fast as the drive signals can be changed. Thus, in one embodiment, a single multiple quantum well device can be used sequentially to emit or reflect light and then to detect the reflected light from the optical disc.
Regardless, the use of such multifunctional devices permits a linear array to be used in the read/write functions so that all information transfer can occur with a single revolution of the optical disc.
In summary, a method and apparatus utilizing a multiple quantum well modulator/emitter/detector pixel in a bilinear array permits reading or writing to an optical disc in parallel such that information may either be written to or read from an optical disc within one revolution of the optical disc. Thus while existing DVD and CDROM systems operate by sensing the contents of a spiral track, parallel readout afforded by the multiple quantum well modulator/emitter/detector provides as much as 1,000:1 advantage over single detector systems, with the biasing of the modulator/emitter/detector device determining whether the device is an emitter, detector or modulator. The co-location of the modulator/emitter/detector in a single device permits arranging devices in a linear array which is disposed over the optical disc for the parallel read/write functions.